Biodiesel cold soak filtering system

ABSTRACT

A system and process of producing a biodiesel product which meets the specifications of the Cold Soak Filtration Test method (ASTM D6751-08).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to 61/161,575, filed Mar. 19, 2009 and incorporated herein by reference.

FEDERALLY SPONSORED RESEARCH

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE INVENTION

The present invention relates to a novel system and process of treating a biodiesel stream. In particular, the present invention relates to the process for producing a methyl ester biodiesel product which meets the specifications of the Cold Soak Filtration Test method (ASTM D6751-08) and significantly reduces the monoglyceride content.

BACKGROUND OF THE INVENTION

Elevated water content and precipitation of trace impurities in biodiesel lead to difficulties with the blending of biodiesel with conventional diesel fuel. Biodiesel needs to meet the specifications set forth in the Cold Soak Filtration Test (CSFT) (ASTM D6751-08). A summary of the test may be described as a representative sample of biodiesel being chilled for approximately 16 hours at about 40° F. (4.4° C.). The chilled sample is allowed to warm to between about 68 to about 72° F. (about 20 to about 22° C.) and filtered under vacuum (between about 21 to about 25 in Hg) through an approximate 0.7 μm pore size 47 mm diameter glass microfiber filter. The time for complete filtration of the sample is recorded to the nearest second. For biodiesel to be blended with diesel fuel the requirements for use at temperatures of about −12° C. (about 10.4° F.) and below is 200 seconds and 360 seconds for biodiesel to be blended with diesel fuel for use at temperatures equal to or greater than about −12° C.

Some potential processes for removing the water and impurities include washing crude biodiesel with glycerin, using a flocculating aid, increased water washing, more precise filtration, and cooling and filtering as well as use of a solid acid catalyst filter. Increased water washing removes the impurities, but the excess water required is significant (triple or quadruple the amount of water typically used along with longer overall cycle time) thus making the process impractical and not cost effective. Filtration alone does not improve biodiesel cold soak filtration times sufficiently for the biodiesel to meet specification. Use of only solid acid catalyst resin had excessive regeneration requirements. All of these processes for removal of water and impurities either failed or were not practical due to cost or other constraints. Distillation of biodiesel has been shown to be effective, but the high capital cost, high energy input required and excessive losses in the distillation bottoms make it a very expensive option.

A process for producing biodiesel methyl esters which meets the specifications of the Cold Soak Filtration Test method (ASTM D6751-08) and is cost effective is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic presentation for an embodiment of a system for treating biodiesel.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a novel system and process of treating a biodiesel stream. Unless otherwise specified, all quantities, percentages and ratios herein are by weight. Materials for the equipment of the process may be carbon steel, more preferably stainless steel. In particular, heat exchangers are stainless steel.

Referring to FIG. 1, biodiesel 1 is cooled via a heat exchanger 10 producing a cooled biodiesel 2. The cooled biodiesel 2 temperature ranges from about 40° F. to about 80° F. (4 to about 26.7° C.), more preferably from about 3 to about 5° F. (about 2 to about 3° C.) above the cloud point of the biodiesel 1. The biodiesel 1 starting temperature ranges from about 85 to about 120° F. (about 29.4 to about 48.9° C.). In a preferred embodiment, the temperature of the biodiesel 1 is about 105° F. (about 40.6° C.) after exiting a vacuum dryer or a waterless method of producing methyl esters. The temperature of the cooled biodiesel 2 exiting the heat exchanger 10 ranges from about 40° F. to about 80° F. (about 4.4 to about 26.7° C.), dependent upon the temperature of biodiesel 1 entering heat exchanger 10.

The biodiesel 1 may be produced from any vegetable, plant or animal fat or oil. In some embodiments, the biodiesel 1 is produced from tallows, palm and palm oil blends, soy, canola, rapeseed, camelina, sunflower seed oil, cottonseed oil, algae oils, yellow grease and poultry fats. The biodiesel 1 preferably has a total glycerin number not exceeding 0.24% weight as determined by ASTM D6584.

The heat exchanger 10 may be any type of heat exchanger which can cool the biodiesel 1 to the desired temperature of the cooled biodiesel 2. In a preferred embodiment, the heat exchanger 10 is a pair of heat exchangers, a first exchanger and a second exchanger sequentially arranged. The first exchanger acts as an economizer and pre-cools the biodiesel 1 with a treated biodiesel 5. The first exchanger typically lowers the temperature of the biodiesel 1 from between about 120° F. and about 85° F. to between about 75° F. and about 60° F., dependent upon the temperature of biodiesel 1 entering the first exchanger. The second exchanger typically uses a chilled heat transfer fluid to further lower the temperature of the biodiesel to between about 40° F. and about 75° F., depending upon the temperature drop achieved in the first exchanger and adjusted for the cold flow characteristics of individual feedstocks used to produce the biodiesel. The second exchanger preferably uses a propylene glycol/water chiller fluid but any of a wide variety of known heat transfer fluids could be used. In alternative embodiments of the invention, one or more heat exchangers may be utilized.

In some embodiments of the invention, the cooled biodiesel 2 is directed to a retention tank 20. The retention tank 20 is preferably sized to hold the cooled biodiesel 2 for about 2.5 to about 5 hours. In some embodiments, longer retention time promotes precipitation and density phase separation of impurities. The retention time may be adjusted to allow for precipitation of impurities in the cooled biodiesel 2, including impurities such as sterol glucosides and monoglycerides. In some embodiments, retention tank 20 is a continuous flow tank, that is there is a continuous flow entering into the tank, where the product enters the bottom of the tank and exits from the top, giving the desired retention time to allow for precipitation of the impurities.

In some embodiments, the chilled biodiesel 3 is directed from the retention tank 20 to a chilled biodiesel filter 30 to produce a filtered biodiesel 4. Typically, the chilled biodiesel 3 is filtered to target 95% removal of particles based on particle size distribution of the chilled biodiesel. The filter pore size may range from between about 1 micron to about 20 microns. In a preferred embodiment, the filter pore size ranges from between about 1 to about 5 microns. In a preferred embodiment, the chilled biodiesel 3 is filtered to remove about 95% of particles greater than about 1 micron in size. The chilled biodiesel filter 30 is any filter capable of filtering to the required pore size, such as but not limited to cartridge and sock filters. In a preferred embodiment, the chilled biodiesel filter 30 is a multiunit sock filter sized to handle a flow rate of chilled biodiesel 3 at a sufficiently low approach velocity that the filter porosity is compacted with solids in a short interval of time, thus allowing a sufficient interval of operating time between filter changes or cleaning.

The filtered biodiesel 4 is passed through an ion exchange resin vessel 40 to produce a treated biodiesel 5. In a preferred embodiment, there are two ion exchange resin vessels arranged in a lead-lag arrangement and a third vessel that can be placed into service while regenerating any one other vessel that was serving in the lead positon. The ion exchange vessel 40 is typically filled with a solid acid catalyst. The solid acid catalyst preferably has sites with an affinity for binding residual impurities in the filtered biodiesel 4. In a preferred embodiment, the impurities include sterol glucosides, monoglycerides, water, soap, free glycerin and metals.

The solid acid catalyst may be any macroporous strong acid resin catalyst able to absorb hydroxyl groups of organic compounds. In a preferred embodiment, the strong acid resin catalyst is dry. In some embodiments, the strong acid resin catalyst is a DOW BDA-35 dry resin. In alternate embodiments, the strong acid resin catalyst may be Rohm & Haas A-35 (dry), BD-20 (dry), Dowex DR-2030 (dry) or Dowex Monosphere DR-2030 (dry). The wet forms of solid acid catalyst resins may also be used. If a wet form of a solid acid catalyst resin is used, in some embodiments, the resin is dried prior to placing into service.

Exiting ion exchange vessel 40 is treated biodiesel 5 which may then be passed through heat exchanger 1 to produce a heated biodiesel 6. In some embodiments, the temperature of the heated biodiesel 6 has the final product storage temperature, ranging from about 70 to about 120° F., more preferably from about 95 to about 100° F. In some embodiments, the heated biodiesel 6 is sent through a finishing filter 50. The finishing filter 50 preferably removes any solid acid resin catalyst fines present in the treated biodiesel 5 to produce a final product 7. In preferred embodiments, finishing filter 50 removes about 95% of particles based on particle size distribution of the product. The finishing filter may have a pore size of between about 1 and about 5 microns, and in a preferred embodiment has a pore size of about 1 μm.

The final product 7 meets the specifications of the Cold Soak Filtration Test method (ASTM D6751-08). The final product 7 has reduced amounts of sterol glucosides and the monoglyceride content of the biodiesel 1 is reduced from as high as about 0.8% down to less than about 0.4 wt %, preferably about 0.15 wt %, and in some cases after regeneration to about 0.01%. More frequent regeneration can be used to maintain very low concentrations of monoglycerides. Monoglyceride content is measured using an FID gas chromatograph with ASTM method D6584. Typical water content for the final product 7 ranges from about 39 ppm to about 159 ppm.

When the resins in the ion exchange vessel 40 are exhausted, they may be regenerated using IMPCA grade methanol to remove sterols and monoglycerides that are bound to the resin. To regenerate, the ion exchange resin vessel 40 is purged with methanol 8. The resins are washed with approximately three (3) bed volumes of methanol over about six (6) hours. The resin beds of the ion exchange resin vessel 40 are then purged of methanol and flushed with two (2) bed volumes of filtered biodiesel 4 prior to being placed back into service.

Although various embodiments of the method and apparatus of the present invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth herein. 

1. A method of treating a biodiesel stream containing impurities comprising: (a) cooling the biodiesel stream to a temperature ranging from about 40 to about 80° F. to produce a cooled biodiesel stream; (b) storing the cooled biodiesel stream from between about 2.5 and about 5 hours to produce a retained biodiesel stream; and (c) passing the retained biodiesel stream through an ion exchange resin to produce a treated biodiesel stream, wherein the treated biodiesel stream meets the specification of the Cold Soak Filtration Test method (ASTM D6751-08).
 2. The method of claim 1 wherein the biodiesel stream containing impurities comprises less than about 0.24% weight total glycerin as determined by ASTM D6584.
 3. The method of claim 1 wherein the biodiesel stream containing impurities comprises sterol glucosides, monoglycerides, water, soap, and metals.
 4. The method of claim 1 wherein the biodiesel stream containing impurities is produced from one or more of tallows, palm and palm oil blends, soy, canola, rapeseed, camelina, sunflower seed oil, cottonseed oil, algae oils, yellow grease and poultry fats.
 5. The method of claim 1 wherein the ion exchange resin is a solid acid catalyst capable of binding hydroxyl groups.
 6. The method of claim 1 further comprising filtering the retained biodiesel stream.
 7. The method of claim 6 wherein filtering the retained biodiesel stream comprises removing about 95% of particles having a particle size greater than about 1 micron.
 8. The method of claim 1 further comprising filtering the treated biodiesel stream.
 9. The method of claim 8 wherein filtering the treated biodiesel stream comprises heating the treated biodiesel stream to a temperature between about 70 and about 120° F. and filtering to remove particles having a particle size greater than about 1 micron.
 10. The method of claim 1 wherein the treated biodiesel stream comprises less than bout 0.4 wt % monoglycerides.
 11. The method of claim 1 wherein the treated biodiesel stream comprises less than bout 0.1 wt % monoglycerides. 